Local/remote switching failures are among the most confusing actuator faults: switched to local, the valve still obeys remote; hand-driven to about 10% opening, it "returns" by itself. A Bernard actuator case (12 replies) walks through the full troubleshooting logic.
A Bernard electric control valve, selector switched to local, still responds to remote commands; when hand-driven locally to about 10% opening, the valve "returns" to its previous position by itself.
1. A zero-cost test: disconnect the remote command wires and try local operation. If the "return" disappears, the actuator is still obeying remote — local mode was never engaged (or is overridden by a remote-priority logic). Two remedies: change the remote-priority parameter, or replace the selector switch.
2. The crosstalk analysis (the thread's most valuable reply): after verifying every conductor between remote end and local, and between the control room and the field, operate from remote — if it will not move, the device is at fault; if it moves and reverts whenever you switch to local, then the local and remote terminal blocks are internally crosstalked and the device remains in "remote" state. The "automatic return" is simply the remote signal — usually a full-open/full-close command — continuously driving the valve.
3. The parameter view: check for settings such as "valve closes when switched to local" or "remote mode always valid" — sometimes it is not hardware but a setting that hard-wires remote priority.
4. Grounding and insulation: a fellow engineer describes a near-identical puzzle — valve normal locally while the DCS saw full open/close swings; the valve behaved fine elsewhere; the final culprit was a grounded conductor, cleared and done. His five categories of control-valve faults deserve copying into every notebook: external wiring, internal wiring, settings, command signal, interference.
5. The vendor's view: Bernard's official account points to the handwheel unit or main-board wiring, to be isolated by substituting spares.
1. Disconnect remote command wires, try local (zero cost; instantly answers "is the actuator still remote-driven?")
2. Ring out the whole circuit remote↔local and control-room↔field, hunting crosstalk and grounds
3. Inspect the selector switch itself and remote-priority-type parameters
4. Substitute spares: handwheel unit, selector switch, main board
"Local/remote" is fundamentally an arbitration of control authority. Note the mirror image: this case is crosstalk letting remote override local, while the AUMA article shows insulation faults creating phantom commands. Cable and ground checks remain the best value-for-money tools in actuator diagnostics.
